I see, the problem in this case is that my SSD was disappearing while active (I have my windows 10 installed on it), i was working here and suddenly the screen goes black with the message "Reboot and Select proper Boot device" and the SSD not showing anymore.
I found this post:
[SOLVED] - M2 NVMe SSD sometimes disappears | Tom's Hardware Forum (tomshardware.com)
but since it's closed i couldn't answer with the solution
If you have a Gigabyte Z370m Aorus Gaming MB (or similar), and a NVMe M2 SSD (mine is from XPG), and it keeps disappearing, just...